/Engine/Plugins/Runtime/GameplayAbilities/Source/GameplayAbilities/Public/AbilitySystemComponent.h
Returns multicast delegate that is invoked whenever a tag is added or removed (but not if just count is increased. Only for 'new' and 'removed' events)
[FOnGameplayEffectTagCountChanged](API\Plugins\GameplayAbilities\FOnGameplayEffectTagCountChanged) & RegisterGenericGameplayTagEvent()